A Local Area Network (LAN) is a communication network (or enables computers attached to a network) that spans a relatively small geographic region. Most LANs are confined to a single building or group of buildings. However, one LAN can be connected to one or more other LANs via land-lines or radio waves. A system of LANs connected in this way is called a Wide Area Network (WAN).
Ethernet is presently considered a dominant LAN technology. As a result, a substantial level of the total data traffic associated with LANS terminates at an Ethernet port. There is a continuous demand for ever-faster networking speeds. Ethernet technology is meeting this demand through a combination of modifications and enhancements. For example, Ethernet technology has evolved from a half-duplex shared media at a speed of 10 Mbps in the LAN, to a full-duplex switched 10/100/1000/10000 Mbps in the LAN and Metro Area Networks (MAN). In the near-future, 40 to 100 Gigabit Ethernet speeds are expected to be reached on core backbone links.
Despite these advances, however, Ethernet technology is not presently mature for use in a service provider environment. A service provider offers its Ethernet services to a customer over a User to Network Interface (UNI) and builds logical connections called Ethernet virtual connections (EVCs). Specifically, the use of pure Ethernet as a transport medium in the Metro and Wide area networks still faces several key hurdles including end-to-end Quality of Service (QoS) guarantees. QoS refers to the capability of a network to provide better service to selected network traffic over various technologies, such as Frame Relay, Asynchronous Transfer Mode (ATM), and Ethernet. Currently, Ethernet provides best effort traffic delivery based on Spanning Tree Protocol (STP). A best effort traffic delivery system is a system that makes an attempt to forward all datagrams over a network connection although the outcome is not guaranteed. Thus, if the network becomes overloaded or routes change, datagrams can be lost, delayed or delivered out of order. The lack of inherent QoS capabilities of Ethernet raises the critical issue of whether a given request with a specific QoS requirement can be admitted without compromising the service performance of already accepted Ethernet Virtual Connections (EVCs), which have been provisioned with certain guarantees such as committed information rate (CIR) and excess information rate (EIR). To enhance the performance of best effort delivery systems based on STP, Multiple Spanning Tree (MST) protocol can be used to increase the number of paths upon which data can be transmitted through a network. Having more paths available via MST could reduce loss of data due to capacity limitations of the trunk links. More details of STP and MST protocol are provided below.
Class of Service (CoS) is a form of a service definition set by the service provider that provides certain guarantees and performance metrics. CoS can be mapped to priority queues that have been used in a number of communication and networking protocols. CoS classifies packets by examining packet parameters or CoS markings and places packets in queues of different priorities based on predefined criteria. Native Ethernet has no CoS provision and therefore cannot mark packets for prioritization, scheduling, or policing; however, IEEE 802.1Q tags provide the capability to support CoS but has no control protocol to guarantee it. Typically, a service provider provides several classes of service to support different customer applications. Each CoS is distinguished by its performance guarantees such as delay, packet loss and jitter. For example, Gold service class is defined to support packet voice applications and meet their performance objectives (delay, jitter and packet loss).
Further, Ethernet has a major scalability bottleneck due to its use of Spanning Tree Protocol (STP) for routing traffic. STP is a link management protocol that provides path redundancy while preventing undesirable loops in the network. For an Ethernet network to function properly, only one active loop-free path can exist between two stations. Unfortunately, allowing only one path can result in uneven load distribution and potential bottlenecks. To provide path redundancy, STP defines a tree that spans all switches in an extended network. STP forces certain redundant data paths into a standby (blocked) state. If one network segment in the STP becomes unreachable, or if STP costs change, the spanning-tree algorithm reconfigures the spanning-tree topology and reestablishes the link by activating one of the standby paths. Ethernet path establishment via STP could mean that a non-optimal path exists, which could introduce packet loss, jitter, and delay. Multiple Spanning Tree (MST) protocol addresses STP limitations by allowing more links to be utilized in the network. For example, if a first Ethernet path becomes overloaded due to heavy traffic, MST protocol can establish an alternative loop free path upon which datagrams can travel across, which will result in reducing this traffic on the first Ethernet path. Thus, MST protocol can be used to distribute the traffic across the links and enhance the QoS of a network, but it is not CoS aware.
The next generation of Ethernet services will require guarantees of service performance, typically specified in a Service Level Agreement (SLA). Consequently, for Ethernet to evolve as a next generation networking technology that will continue to dominate LAN technologies as well as to have an increasing share of MAN and WAN technologies, it must support QoS and CoS. Thus, there is a need for an admission control system and method that controls EVC admission into a service provider's network and determines the most efficient path through the network in view of CoS as well as QoS requirements.